Electrical apparatus



Oct. 1l, 1938. J. P. SMITH ELCTRICAL APPARATUS Filed Oct. 18,. 1934 4Sheets-Sheet 1 mm v mi JohnR'mi/th INVEN''OH HTTURNEY Oct. 11, 1938. J.P. SMITH ELECTRICAL APPARATUS 4 Sheets-Sheet 2 Filed 001;. 18, 1934 Fig.6.

Voltage an f z Voltage on G2 INVEN'T'GH John R 5mi 'th y Oct. 1l, 1938.J, p SMH-H 2,132,654

ELECTRICAL APPARATUS Filed OG t. 18, 1954 4 Sheets-Sheet 3 Voltage pn,P2

Voltage on' R3 Voltage on 1.33

Voltage on G2 60N Voltage-on G2 Isl/'5% Q ATTORNEY Oct. 11, 1938.

J. P. SMITH ELECTRICAL APPARATUS 4 Sheets-Sheet 4 Filed Oct. 18. 193460N line 60N output of phase Shifter hase of mvZL'z/ib. dl/PU LS shiftedwith respect to Zine voltage v l rNvE/v'roR John I? 'mi th HTTGRNEY'Patented ocr'. 11, 193s- ELECTRICAL APPARATUS John P. Smith, Erlton, N.J., assignor, by mesne assignments, to Radio Corporation of America, NewYork, N. Y., a corporation of Delaware Application October 18, 1934,Serial No. 748,773

12 Claims.

In a television transmitter which employes a cathode-ray transmittertube, it is necessary to utilize electric impulses occurring at acomparatively high frequency for deflecting the cathode-ray horizontallyand other impulses occurring at a comparatively low framing frequencyfor deflecting the cathode-ray vertically. 'I'hese impulses may begenerated by means of a high speed disc and a photo-electric cell but ithas been found preferable to generate them by means of electricdischarge devices. such as vacuum tubes, whereby all moving parts areavoided.

An object of my invention is to., provide an improved electric dischargetube generator of the above-mentioned type.

A further object of my invention is to provide an improved method of andmeans for operating a plurality of multivibrators in controlled relationto each other.

A further object of my invention is to provide an improved means fordetermining what unit of a tube impulse generator has failed to functionin the event that the generator fails to supply impulses at the properfrequency.

A still further object of my invention is to provide means for shiftingthe phase of the impulses supplied by a tube generator with respect to astandard frequency.

In a preferred embodiment of my invention I employ a chain ofmultivibrators which divide a comparatively high frequency in severalsteps to the desired synchronizing and framing frequencies. T'hemultivibrators are so adjusted with respect to each other that each oneis positively controlled or lockedin by the preceding multivibrator eventhough variations occur in the high` J with an indicator lamp which islighted so long as the multivibrator is operating at the properfrequency. If, for any reason, a particular multivibrator falls out ofstep with the controlling multivibrator, its associated indicator lampis extinguished and the operator knows which one of the severalmultivibrators to readjust In accordance with one feature of myinvention, I provide means for shifting the phase of the output of theimpulse generator with respect to a 60 cycle power line. This isespecially desirable (Cl. Z-36) if the impulse generator is beingemployed in a system which is transmitting pictures from a fllm beingrun through a motion `picture projector. A

Other objects, features, and advantages of my invention will appear fromthe following descrlp- 5 tion taken in connection with the accompanyingdrawings, in which Figure l is a circuit diagram of one embodiment of myinvention,

Fig. 2 is a view of a portion of the control panel for my improvedimpulse generator,

Figs. 3 to 17 are curves which are referred to in explaining theoperation of the multivibrator chain shown in Fig. l, and

Figs. 18 to 21 are curves which are referred to in explaining theoperation of the phase shifting circuit shown .in Fig. 1.

Referring to Fig. 1, there is illustrated an electrical impulsegenerator which is designed to supply horizontal synchronizing impulsesand vertical synchronizing or framing impulses having the properfrequency relation for producing interlaced scanning as described andclaimed in application Serial No. 726,258, filed May 18, 1934, in thename of A. V. Bedford and assigned to the Radio Corporation of America.The impulse generator comprises a multivibrator adjusted to oscillate ata frequency of 20,580 cycles per second and a chain of multivibrators,shown on the right-hand side of the drawings, which divide 30 thefrequency of 20,580 cycles in three steps of '1 to 60 cycles, which isthe frequency desired for vertical deflection or framing. Therefore, themultivibrator chain includes a multivibrator which supplies an outputhaving a frequency of 2,940 cycles, another multivibrator which suppliesan output having a frequency of 420 cycles and the last multivibratorwhich has the 60 cycle output.

The 20,580 cycle frequency of the rst multl- 40 vibrator is divided bytwo by means of another multivibrator, shown on the left hand side ofthe drawings, in order to produce the desired horizontal deflectingfrequency of 10,290 cycles.

Except for the circuit constants, the five multi- 45 vibrators areconstructed alike. In the drawings, each multivibrator is shown ascomprising a vacuum tube T1 and a vacuum tube T2. Actually, in apreferred embodiment, the circuit of which is shown in Fig. 1, theelements of tubes T1 and T2 are in the same glass envelope, the triodeportion of a 6Fl tube being used for a T1 and the pentode portion of thesame 6Fl tube being used for the tube T2.

In order to avoid unnecessary crowding of the drawings, the suppressorgrid of the pentode portion of the 6Fl tube is not illustrated. Thesuppresser grid serves merely as a shielding electrode to reducecapacity coupling between the electrodes Pa and Pa.

'Ihe control grid and the plate of the tube T1 are identified by thereference characters G1 and P1, respectively, whileA the control grid,the screen grid and the plate of the tube T2 are identified by thereference characters G2, P2 and Pa, respectively. The screen grid Pnfunctions as a plate or anode rather than as a screen grid in themultivibrator circuit, while the plate Pa functions as a couplingelectrode for coupling the one multivibrator to a succeedingmultivibrator.

In the drawings, the values of the resistors have been indicated in ohmsandthe values of the capacitors have been indicated in microfarads. Itwill be understood that these values are given for only one specificembodiment of the invention and may be varied within wide limits inother embodiments:

Referring specifically to the 20,580 cycle multivibrator, the indirectlyheated cathodes of the tubes T1 and T2 are connected to ground. Theelectrodes P1 and P2 are connected through 10,000 ohm resistors to a30,000 ohm resistor and through the 30,000 ohm resistor to a suitablepositive voltage supply. The plate end of the 30,000 ohm resistor isconnected to ground through an 8 microfarad by-pass capacitor.

The electrode P1 is coupled to the grid G2 through a .001 microfaradcapacitor while the electrode P2 is connected through another .001microfarad capacitor to the grid G1. The grid G1 is connected to itscathode through a 12,500 ohm variable resistor, while the grid Ga isconnected to its cathode through a 40,000 ohm resistor and 2,000 ohmresistor connected in series.

It will be understood that all variable resistors are set at the valuesshown on the drawings in the particular circuit being described.However, the stability of the circuit is such that they may be variedconsiderably without the multivibrators falling out of step.

The above described circuit functions in a well known manner to produceoscillations having a wave form shown in Fig. 5. This wave shape isproduced by tubes T1 and T2 alternately blocking and unblocking, thecontrol of the tubes being effected by the .001 microfarad capacitorsbecoming charged to bias a tube beyond its cut-off point and thengradually discharging through the grid and plate resistors.

The electrode Ps is supplied with positive potential through a 10,000ohm resistor and a 4,000 ohm resistor connected in series. An 8microfarad by-pass capacitor is connected between the lower end of the4,000 ohm resistor and ground.

Referring to the 2,940 cycle multivibrator, the circuit connections arethe same as described above but certain of the circuit constants havebeen changed both for making the uncontrolled or free running frequencyof the oscillator lower and for making the wave shape of themultivibrator output more unsymmetrical. It will be noted that thecoupling capacitors have been increased in capacity to .005 microfaradand that the resistor coupling the grid G1 to the cathode has beenincreased to 122,000 ohms, while the resistor coupling the grid G2 toits cathode has been decreased in value to 20,000 ohms. Also, the plateP1 and the electrode P2 are coupled to acommon 200,000 ohm resistorthrough a 100,000

ohm resistor and a 20,000 ohm resistor, respectively.

Voltage is supplied to the electrodes P1 and P2 rical wave shapeproduced by the 2,940 cycle unit I will be seen by referring to thecurve in Fig. 4.

It will be noted that the coupling between multivibrators is a result ofthe electro'de`Pa being in the same electron stream as the electrodes G2and Pz, this being referred to as electron coupling.

The 420 cycle multivibrator is the same as the preceding one except thatthe coupling capacitors have been increased in capacity to .05microfarad, while the resistor connecting the grid G1 to its cathode hasbeen given the comparatively low value of 7,600 ohms and the resistorconnecting the grid G2 to its cathode has been given the comparativelyhigh value of 105,000 ohms. The 420 cycle multivibrator is connected tothe electrode P: of the preceding multivibrator through a conductor IIand a 100,000 ohm resistor.

The cycle multivibrator is the same as the 420 cycle multivibratorexcept that the coupling capacities have been increased in value to .25microfarad, while the resistor connecting the grid G1 toits cathode hasbeen given the comparatively high value of 46,500 ohms and the resistorcoupling the grid Ga to its cathode has been given the comparatively lowvalue of 5,000 ohms.

Particular attention is called to the fact that if, in onemultivibrator, the grid resistor for tube T1 is higher than the gridresistor for tube T1 in the succeeding multivibrator the grid resistorfor tube T1 is lower than the grid resistor for tube T2. This circuitarrangement is employed for the purpose of reversing the phase inalternate multivibrators as will be described in detail later inconnection with the description of the multivibrator operation.

The 10,290 cycle multivibrator which supplies the horizontal detlectingimpulses is similar to 'the previously described multivibrators and iscoupled to the electrode P3 of the 20,580 cycle unit through a 200,000ohm resistor.

In the past, it was found that a chain of frequency dividers orfrequency multipliers was very diftlcult to operate for the reason thatif one unit of the system fell out of step, the operator could bring theoutput of the system back to the desired frequency only by adjustingvarious units in the system until the system as a whole was againoperating properly. As a rule, this was a very tedious procedure. Inaccordance, therefore, with one feature of my invention I provide the20,580 cycle oscillator and each frequency divider unit with afrequency-indicator which includes a neon lamp that remains lighted solong as the oscillator or frequency divider is operating at the correctfrequency.

The circuit of the frequency indicator connected to the 10,290 cyclemultivibrator is shown in detail while the frequency indicatorsconnected to the other units are indicated schematically. Referring tothe 10,290 cycle indicator, it comprises an electric discharge tube I3which may be of the screen grid type having a cathode I5, a control gridI1, a screen grid I9 and a plate 2l. The

-Pa of .the 10,290 cycle unitgthrough a resistor and coupling capacitor21. y'The screen grid I9 is supplied with a suitable positive potentialthrough a resistor 29, a bleeder resistor 3| being connected between thescreen grid and cathode. A suitable by-pass capacitor 33 is connectedbetween the screen grid I9 and ground.

'Ihe plate circuit of the tube I3 includes a parallel resonant circuitconsisting of an inductance coil 35 and a capacitor 31 tuned to thefrequency of 10,290 cycles. The plate 2| is supplied with a positivepotential through a plate resistor 39 and through the inductance coil35, a by-pass capacitor 4| being connected' between the upper end of theresistor 39 and ground. A gaseous discharge device such as neon glowtube 43 is connected across the parallel resonant circuit in series witha resistor 45 which has a resistance value sufficiently high to preventthe 'neon tube from loading the tuned circuit too much when the'glowtube breaks down.

In operation, if the 10,290 cycle multivibrator is operating to give anoutput having the frequency of 10,290 cycles, a voltage of thatfrequency appears across the parallel resonant circuit having amagnitude great enough to break down the neon tube 43 and cause it toglow. If the frequency of the multi-vibrator output changes, the voltageacross the tuned circuit drops to a low value and the glow tube isextinguished. Thus it will be seen that if the system is operating'properly, all the neon tubes 43 of the several frequency indicators willbe lighted, but that if any multivibrator unit falis to provide anoutput of the proper frequency, the neon tube corresponding to that unitwill be extinguished. The operator immediately knows which multivibratorunit must be readjusted and it is a simple matter to again put thesystem in operation. i

Fig. 2 shows a preferred control panel layout for the multivibratorcontrols and frequency indicator lamps 43. The indicator lamp for eachmultivibrator is mounted directly above the control knob 41 for thatmultivibrator. vibrator control knobs 41 are for varying the values ofthe variable grid resistors indicated in Fig. 1, the knob positionedbelow the meter 49 being the control knob for the 20,580 cycle unit, andthe control knob for the 10,290 cycle unit being at the left of themeter 49. In operation, if the neon lamp above the control knob 41 ofthe 10,290 cycle unit is extinguished, for example,

that control knob is turned until the neon lamp again lights.

The operation of the multivibrator chain will now be described withspecial reference to the 2,940 cycle unit. Figs. 3, 6, 1, 10 and 11 arere'- productions of actual curves that were obtained by means of anoscillograph which was connected between ground and the variouselectrodes of the 2,940 cycle multivibrator in the multivibrator chainillustrated in the drawings.

Fig. 3 is a curve of the voltage which was observed on the control gridG1 on the 2,940 cycle unit. This voltage wave is the sum of the voltagewave produced by the 2,940 cycle unit and the voltage wave produced bythe 20,580 cycle unit. These two components of the voltage observed onthe G1 are illustrated in Figs. 4 and 5.

` It will be understood that ythe solid line curve 'I'he multithe higherfrequency unit and is not exactly the same voltage wave as would beproduced if the unit were running free or uncontrolled. It will be notedthat the positive impulses .are much narrower than the negative impulsesdue to the 5 fact that one grid resistor in the multivibratoryhas a muchlarger value than the other grid resistor.

The curve shown in Fig. 5 represents the voltage output of the 20,580cycle unit, this unit bel0 ing free running except for the controlprovided from a 60 cycle power line through a circuit which will bedescribed hereinafter.

By referring to the drawings, it will be seen that the 20,580 cycleimpulses are applied tothe 15 grid G1 of the 2,940 cycle unit throughone of the coupling capacitors and that the same impulses are applied tothe grid G2 through the other coupling capacitor. Since the two plateresistors in the multivibrator unit have different values, 20 thesynchronizing impulses are not balanced out even though they are appliedto the grids Gi, and G2 simultaneously.

The two voltage components appearing upon the grid ,G1 combine toproduce the slotted 2,940 25 cycle voltage wave. 'Ihese slots areindicated by the dotted line portions in Fig. 4 and are clearly shown inthe actual curve in Fig. 3.

A curve of the voltage observed on the plate Pi is shown in Fig. 6. Aswould be expected, in 30 this curve the narrow impulse is in a downwardor negative direction while the wide impulse is in an upward or positivedirection. The phase of the slot in the narrow impulse is also reversedbut the'phase of the slots in the wide impulse 35 has not been reversed,the narrow slots being in a downward direction just as in Fig. 3. Thereason that the phase of the slots is not reversed in the wide impulseis that during this period the tube T1 is blocked so that the slotsappearing on 40 the wide impulses are due to 20,580 cycle impulses beingimpressed directly upon the plate P1. 'I'he particular slopes at thebottom and top of the negative and positive impulses, respectively,might not be expected and it is believed that they 45 are the result ofa coupling capacitor being effectively in shunt to the 100,000 ohm plateresistor whereby a certain amount of time is required for the capacitorto receive a full charge.

` In Fig. 7 there is shown a curve of the voltage 50 observed on thegrid G2. This is probably the most important of the voltage curves whichwere observed as it is believed that this curve shows the manner inwhich one multivibrator is held in step with a preceding multivibrator.It would be 55 expected that the voltage appearing `on Ga would have thesame phase as the voltage appearing on Pr since the two electrodes arecoupled together through a coupling capacitor. It will be seen that thisis true of both the 2,940 cycle component 60 and the 20,580 cyclecomponent which is producing the slots.

In Figs. 8 and 9 are shown the 2,940 cycle component and the 20,580cycle component of the voltage Wave illustrated in Fig. 7. By referringto 35 Fig. 1, it will be seen that the controlling impulses from thehigher frequency multivibrator are impressed upon the grid G2 throughtwo paths. They are impressed upon G2 directly through the 100,000 ohmresistor and a .005 microfarad coupling capacitor and they are impressedIupon the grid G1 through another path comprising the 20,000 ohm plateresistor, the other .005 microfarad coupling capacitor, the tube T1 andthrough the first coupling capacitor to 75 the grid Ga. Impulsestraversing the first path are not amplified while the impulsestraversing the other path are amplified by the tube T1 when it is in anamplifying condition, that is, when it is not blocked.

What is believed to be the method by which the multivibrators are lockedin step will now be described with reference to Fig. 7. If the 2,940cycle multivibrator were free running, the negative impulse would have awidth indicated by the dotted line curve i. The horizontal dotted line53 represents the cut-off point of the tube T1. As is well known, in afree running multivibrator, the width of the negative impulse isdetermined by the time required for the charge of a coupling capacitorto leak olf through a grid resistor to a value such that the controlgrid potential is brought to a value just above the cutoff point. Atthis time the tube starts to amplify and the positive impulse isstarted.

When the multivibrator is operated in the controlled condition, thevoltage on a control grid is changed by an incoming impulse whereby thepositive impulse is started before the coupling capacitor has time todischarge sulciently to bring the voltage on the control grid above thecut-off point.

It will be understood that while tube T2 is blocked to produce the.narrow negative impulse, shown in Fig. '7, the tube T1 has platecurrent flowing therethrough and is in an amplifying condition.Therefore, the narrow negative synchronizing impulses from the 20,580cycle unit which are impressed through a .O05 microfarad couplingcapacitor upon G1 cause a reduction in the plate current of the tube T1whereby they appear amplified and in reversed phase relation uponthe'grid G1.

In the circuit just illustrated, two of these synchronizing impulsesappear while the negative impulse is being produced by the 2,940 cycleunit. As will be seen by referring to Fig. 7, the first impulse does notreduce the negative voltage on G2 sufficiently to bring it above thecut-off point. The second impulse, however, does bring it beyond thecut-off point and at the beginning of this second synchronizing impulsethe positive 2,940 cycle impulse begins.

During the flow of plate current in T2, T1 is blocked whereby it cannotamplify synchronizing impulses and the only synchronizing impulsesappearing upon G2 are those impressed directly through the 100,000 ohmresistor and the .005 microfarad coupling capacitor, these, of course,being in opposite phase to the preceding ones which were amplified bythe tube T1.

In Fig. there is illustrated the wave shape of the voltage which wasobserved on the electrode P1 of the 2,940 cycle multivibrator. It willbe seen that this curve has the same relation to the voltage curve forG2 as the curve for voltage on P1 has to the voltage curve for G1.

In Fig. 11, there is shown the curve for the voltage observed on theelectrode P3 of the 2,940 cycle multivibrator. It will be evident thatthis curve is substantially the same as the curve for voltage on G2except that it is 180 degrees out of phase. Also the peaks of thepositive impulses have been clipped off due to the fact that the tubeoperates at plate current saturation.

The 420 cycle multivibrator is so adjusted that the voltage appearing onits electrode P3 is 180 degrees out of phase with respect to the voltageoutput of the preceding multivibrator as will be seen by comparing Figs.11 and 12. The voltage appearing on the grid G: of the 420 cyclemultivibrator is shown in Fig. 13 while the 2,940 cycle controllingimpulses are shown in Fig. 14. As in all the other figures, the curvesof Figs. 13 and14 are drawn on the same time axis so that the phaserelation of the impulses is shown. It will be seen that the narrowcontrolling impulses are in the same direction as the narrow impulsesappearing on the grid Ga of the multivibrator which is to be controlled.A comparison of Figs. 8 and 9 will show that this is the adjustment forthe 2,940 cycle multivibrator also. This is the preferred adjustment forthe multivibrator chain in order to obtain the greatest stability ofoperation.

It is because this adjustment is desired that the 420 cyclemultivibrator is adjusted to make its output 180 degrees out of phasewith the output of the preceding multivibrator. In a similar manner the60 cycle multivibrator is so adjusted that its voltage output is 180degrees out of phase with the voltage output of the 420 cyclemultivibrator as will be seen by referring to Fig. 15.

The proper phase relation between the controlling impulses and theimpulses to be controlled could be obtained by interposing an amplifiertube between multivibrators for the purpose of reversing the phase ofcontrolling impulses. In my circuit I have obtained the same effect witha considerable saving in vacuum tubes by making the grid resistor forthe tube T1 greater than the grid resistor for the tube T1 in alternatemultivibrator stages and by making the grid resistor for the tube Tagreater than the grid resistor for the tube T1 in the remaining stagesas indicated in Fig. 1. t

A comparison of Figs. 16 and 17 will show that in the 60 cyclemultivibrator the narrow controlling impulses are in the same directionas the narrow impulse on the grid G2 Just as in the precedingmultivibrators.

In the 60- cycle multivibrator the narrow impulse has been madesumciently narrow to prevent a controlling impulse from beingsuperimposed thereon. By referring to the curvesfor the precedingmultivibrator stages it will be seen that the narrow impulse of thevoltage output of the multivibrators has a slot therein which wasproduced by one of the controlling impulses. It has been found inpractice that there is a satisfactory lock-in of the multivibrators withone slot or irregularity on the controlling impulse. However, if thenumber of slots or irregularities on an impulse is increased there is adecided tendency for the multivibrator chain to be unstable. This lackof stability appears to be a result of the multivibrator which is beingcontrolled jumping back and forth from one irregularity to another onthe controlling impulse.

It may be desirable to adjust certain stages of the multivibrator chainfor the greatest stability of lock-in, this being an adjustment such asillustrated in Figs. to 17 where the narrow impulse of the multivibratorbeing controlled has a width less than the interval betweensynchronizing impulses. It will be seen that this prevents the formationof an irregularity on the impulse appearing in the 60 cyclemultivibrator output whereby it would be especially suitable forsynchronizing another multivibrator.

It may be stated that, although the curvesfor the 2,940 cyclemultivibrator were obtained by means of an oscillograph, the curves forthe other multivibrators are simplified curves which have been drawnmainly to show the polarity and width of the voltage impulses.

Attention is called to the fact that my method of coupling the outputcircuit of one multivibrator to a succeeding multivibrator not onlyprovides a very positive-lock-in of the multivibrators but it alsocompensates to a considerable degree for variations in the amplitude ofthe voltage supply. The compensation is provided because of the flow ofplate current through the coupling resistors, any increase in platevoltage causing the plate current to increase a certain amount wherebythe voltage drop in a coupling resistor is increased and the increase involtage on the electrodes P1 and P2 is caused to bev a minimum. Thismethod of coupling also is desirable since there is no phase shift orchange in amplitude in the transfer of an impulse through the couplingcircuit whereby the 60 cycle regulator circuit, which will now bedescribed, always exercises the proper control over the multivibratorchain.

For some applications of my impulse generator it may be desired tocontrol the phase of its output with respect to the 60 cycle current ofa. power line. Such a phase control may be obtained by means of theregulator circuit illustrated in Fig. 1. In the particular embodimentillustrated, the regulator circuit includes a rectifler tube 60 whichmay consist of a three element vacuum tube having a cathode 6|, a grid62 and a plate 64. The output circuit of the rectiiler is coupledthrough a filter 63 to the 20,580 cycle multivibrator while the inputcircuit is supplied with both 60 cycle current from a power line (notshown) and 60 cycle impulses from the output circuit of the 60 cyclemultivibrator.

The circuit through which the 60 cycle impulses are supplied to therectiiier 60 includes an amplier tube 65 which may be a vacuum tube ofthe three element type having its input circuit coupled through acoupling capacitor 61 to the electrode P3 of the 60 cycle multivibrator.The plate of the amplifier tube 65 is supplied with positive potentialthrough two resistors 69 and 1| connected in series, the pointintermediate the two resistors being connected to the cathode of thetube 65 through a by-pass capacitor 13.

The output circuit of the amplifier tube 65 is coupled to the inputcircuit of the rectier tube 60 through a phase-shifting network whichlincludes a transformer 15 having a primary winding 11 and a secondaryWinding 19. The secondary Winding 19 is connected in series with aresistor 8| and a capacitor 83. The point intermediate the resistor 8|and the capacitor 83 is connected to the plate of the amplifier tube 65while the mid-point of the secondary winding 19 is connected to theinput of the rectifier 60 through a coupling capacitor B5. The primarywinding 11 is connected to a 60 cycle power line (not shown).

The phase of the 60 cycle current appearing across the output terminalsof the phase-shifting network may be varied with respect to the 60 cyclecurrent supplied to the primary winding from the line by varying thevalue ofthe rsistor 8|. It may be noted that this phase shift isproduced wi'hout changing the amplitude of the 60 cycle current. It isdesired that the 60 cycle current from the phase shifter and the 60cycle im.- pulses appearing in the, output circuit of the tube 65 shalladd in the input circuit of the rectier 60.

In order that the outputs of the phase shifter and tube 55 shall add inthe positive direction it is necessary, in effect, to reverse the phaseof the impulse appearing in the output circuit of tube 65 since thistube has reversed the phase of thefjeositive impulse impressed upon itby the 60 cycle multivibrator. This phase reversal is accomplished bymeans of the .25 microfarad capacitor 80 connected between the plate oftube 65 and ground. The action of the capacitor will be explained laterwith reference to Figs. 18

to 2l.

, Referring now to the manner in which the output circuit of therectifier 60 is coupled to the 20,580 cycle multivibrator, it will beseen that the plate circuit of the rectifier tube may be traced from thecathode 6| to ground, through ground to the 2,000 ohm resistor in thegrid circuit of the multivibrator tube T2, through the,

2,000 ohm resistor and through filter resistors 81 and 89, the meter 49and a plate supply battery 9| to the rectier plate 64. The purpose ofthe lter in the rectifier output circuit is to illter out any 60 cyclecomponent which may appear in that circuit whereby only pure directcurrent is supplied by the rectifier tube to the 2,000 ohm multivibratorresistor.

The operation of the phase control circuit will be understood byreferring to Figs. 18 to 21. The curve in Fig. 18 represents the 60cycle current which is supplied from the power line. In Fig. 19, the 60cycle output of the phase-shifting network is indicated by the sine wavecurve 93, in this instance the phase-shifting network being set so thatits output is in phase with the line current.

The 60 cycle impulses which the multivibrator causes to appear in theplate circuit of the tube 65 are indicated by the curve 95. The voltagewhich appears across the capacitor 80 has substantially a saw-tooth waveform as shown by the curve 96. The positive portion of this saw-toothvoltage adds to the positive half cycle of the sine wave voltage in theinput circuit of the rectier tube 60 to give a voltage of the magnitudeindicated by the dotted line 91. The negative half cycles of thevoltages are not passed by the rectifier since it is biased to cut-off.

The direct current output of the rectier tube 60 has a Value dependingupon the magnitude of the voltage applied to the rectifier grid circuit,and the bias voltage applied to the grid G2 of the 20,580 cyclemultivibrator, in turn, has a magnitude depending upon the magnitude ofthe output current of the rectifier. It will be understood that, if therectifier output causes the grid G2 to become more negative, thefrequency of the multivibrator will be lowered momentarily while, if therectiiler output decreases, the frequency of the multivibrator will tendto increase. 1

Fig. 19 represents an equilibrium condition where the multivibratorchain is controlled by a 60 cycle power line, the electrical impulsesappearing in the output circuit of the multivibrator chain having acertain fixed phase relation with respect to the 60 cycle current of theline.

If the resistor 8| in the phase shifter is changed to shift the phase ofthe 60 cycle current appearing across the phase shifter terminals, asindicated by the curve 93 in Fig. 20, the sum of the 60 cycle voltageand the saw-tooth voltage will be decreased as indicated by the dottedline curve 99 whereby the output of the rectifier 60 will be decreasedand the 20,580 cycle multivibrator will.

be speeded up momentarily until the multivibrator impulses assume adifferent position with respect to the 60 cycle line current asindicated in Fig. 21. It will be understood that the multivibratorimpulses will shift to such a phase relation with respect to the 60cycle output of the phase shifting network that an equilibrium conditionis again reached where the sum of the voltages represented by the dottedline curve IUI is the same as for the condition shown in Fig. 19 and themultivibrator chain is again operating in a xed phase relation withrespect to the 60 cycle line. The condition shown in Fig. 20 is greatlyexaggerated, of course, since the multivibrator impulses follow thechange in phase of the 60 cycle sine wave very closely.

The use of a rectifier tube for controlling the frequency of a vacuumtube impulse generator with respect to a power line is described andclaimed in application Serial No. 729,730, iiled June 9, 1934, in thename of A. V. Bedford and assigned to Radio Corporation of America.

In the claims, expressions such a a plurality of tubes or a pair oftubes are to be construed as including a single envelope having two ormore sets of electrodes therein as in a tube of the 6Fl YDC- From theforegoing description it will be understood that various modificationsmay be made in my invention without departing from the spirit 'and scopethereof and I desire,'therefore, that only such limitations should beimposed thereon as are necessitated by the prior art and set forth inthe appended claims.

I claim as my invention:

1. In combination, a plurality of multivibrators, each multivibratorbeing an oscillator of the type comprising two electric discharge tubes,each of said tubes having an anode circuit coupled to the grid circuitof the other tube by resistance coupling, each multivibrator beingadjusted to produce narrow and wide impulses alternately with respect toan alternating current axis, said multivibrators being connected incascade with alternate multivibrators having the narrow impulsesappearing in their output circuits with a polarity which is the oppositeof the polarity of the narrow impulses appearing in the output circuitsof the other multivibrators, whereby the ratio of the frequencies ofsaid cascaded multivibrators is kept substantially constant.

2. A multivibrator chain for obtaining frequency division whichcomprises a multivibrator, said multivibrator being an oscillator of thetype comprising two electric discharge tubes, each of said tubes havingan anode circuit coupled to the grid circuit of the other tube byresistance coupling, said multivibrator being adjusted to produce narrowand wide impulses alternately with respect to an alternating currentaxis and at a certain frequency when fre-running, an output circuit forsaid multivibrator, and means for inbeing an oscillator of the typecomprising two` electric discharge tubes, each of said tubes having ananode circuit coupled to the grid circuit of the other tube byresistance coupling, each multivibrator being so adjusted that itproduces narrow impulses and wide impulses alternately with respect toan alternating current axis. and means for so connecting saidmultivibrators in cascade that the narrow impulses which are impressedupon a certain multivibrator from a preceding multivibrator have apolarity which is the opposite of the polarity of the narrow impulses inthe output of said certain multivibrator, whereby the ratio of thefrequencies of said cascaded multivibrators is kept substantiallyconstant.

4. In combination, a multivibrator comprising an electric discharge tubehaving an input circuit including a control grid and an output circuitincluding an anode and a second electric discharge tube having an inputcircuit including a control grid and an output circuit including ananode, each of said anodes being connected through an impedance unit toa source of potential whereby each tube has a plate or anode current,the grid of each tube being coupled to the anode of the other tube, saidmultivibrator being adjusted to produce narrow and wide impulsesalternately with respect to an alternating current axis, and means forintroducing synchronizing impulses into said anode circuits in suchphase that they have the same polarity as the said narrow impulses whichappear in said grids.

5. In combination, a multivibrator comprising two electric dischargetubes, each having a grid circuit and a plate circuit, the grid circuitof each tube being so coupled to the plate circuit of the'other tubethat oscillations are produced, one of said tubes including anadditional electrode positioned in the same electron stream as the gridand plate of said one tube, a second multivibrator comprising twoelectric discharge tubes having grid circuits and plate circuits coupledto produce oscillations, each of said last mentioned plate circuitsincluding a plate resistor, said plate resistors being connected to saidadditional electrode through a coupling resistor, and an impedance unitconnected to said additional electrode through which voltage may besupplied both to said electrode and to said last mentioned platecircuits.

6. In combination, a multivibrator comprising a pair of electricdischarge tubes, each tube having an input circuit including a grid andan output circuit including an anode, the grid of each tube beingcoupled to the anode of the other tube, one of said tubes having anadditional electrode in the same electron stream as its grid and anode,an impedance unit connected to said additional electrode through whichvoltage may be supplied, a second multivibrator comprising a pair ofelectric vdischarge tubes, each having an input circuit including a gridand an output circuit including an anode, the grid of each tube in saidsecond multivibrator being coupled to the anode of the other tube insaid second multivibrator, one of said last-mentioned anodes beingconnected to said additional electrode through a resistor adjacent tosaid one anode and a second resistor in series, and the other of saidlast-mentioned anodes being connected to said additionalelectrodeggthrough another resistor adjacent to said other anode andthrough said second resistor, the said resistors adjacent to said anodesbeing unequal in value.

'1. Apparatus according to claim 6 characterized in that said secondmultivibrator is adjusted to produce narrow and wide impulsesalternately with 'respect to an alternating current axis and is lockedin on an odd sub-harmonic of the output of said first multivibrator.

8. Apparatus according to claim 6 characterized in that said secondmultivibrator is so adjusted that it produces narrow and wide impulsesalternately with respect to an alternating current axis with the narrowimpulse occurring in the same direction as the narrow impulses from saidfirst multivibrator appearing upon said additional electrode during thewide impulses.

9. In combination, a multivibrator, said multivibrator being anoscillator of the type comprising two electric discharge tubes, each ofsaid tubes having an anode circuit coupled to the grid circuit of theother tube by resistance coupling, said multivibrator being so adjustedthat it has an output of such wave shape that narrow and wide impulsesare produced alternately with respect to an alternating current axis ata certain frequency, and means for impressing synchronizing impulsesupon said multivibrator which occur at a frequency which is an oddharmonic of said certain frequency, said narrow impulses having a widthwhich is no greater than the width of a synchronizing impulse plus twicethe interval between successive synchronizing impulses.

10. In combination, a multivibrator, said multivibrator being anoscillator of the type comprising two electric discharge tubes, each ofsaid tubes having anV anode circuit which is coupled to the grid circuitof the other tube by resistance coupling, said multivibrator being soadjusted that it has an output of such wave shape that narrow and wideimpulses are produced alternately with respect to an alternating currentaxis at a certain frequency, and means for impressing synchronizingimpulses upon said multivibrator which occur at a frequency which is anodd harmonic of said certain frequency, said narrow impulses having awidth which is no greaterthan the interval between successivesynchronizing impulses.

11. In an impulse generator, a plurality of multivibrators connected incascade and indicator means connected with each of said multivibratorsfor indentifying the multivibrator unit which has fallen out of step inthe event that the multivibrator chain fails to function properly, saidindicator means comprising an amplifier tube having a plate circuittuned to said desired frequency, and a glow lamp and impedance unitconnected in series across said tuned circuit.`

12. In combination, an oscillator, a source of current having a controlfrequency, means for deriving voltage from said oscillator having a.frequency equal to said control frequency, a rectifier, an adjustablephase shifting network, means for passing said control frequency currentthrough said network whereby a control frequency voltage appears at theoutput terminals of said network, means for adding said derived voltageand the voltage appearing at the output terminals of said network andimpressing them upon said rectifier, and means for so controlling thefrequency of said oscillator in accordance with the amplitude of saidrectifier output that the phase of said derived voltage may be shiftedwith respect to said control frequency current.

JOHN P. SMITH.

